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A ZnO NR decorated PVDF-MXene composite NF EMI shielding material exhibiting superb absorption dominant EMI SE, flexibility, and multi-functionality.

A flexible piezoelectric composite is composed of a polymer matrix and piezoelectric ceramic fillers to achieve good mechanical flexibility and processability. The overall piezoelectric performance of a composite is largely determined by the piezoelectric filler inside. Thus, different dispersion methods and additives that can promote the dispersion of piezoelectric ceramics and optimal composite structures have been actively investigated. However, relatively few attempts have been made to develop a filler that can effectively contribute to the performance enhancement of piezoelectric devices. In the present work, we introduce the fabrication and performance of the composite piezoelectric devices composed of Li-doped ZnO nanowires (Li: ZnO NWs) grown on the surface of MXene (Ti

This paper describes a facile method for the design and fabrication of hierarchical nanopatterns via aluminum anodization with an application for creating plasmonic crystals. Fabrication of highly-ordered anodized aluminum oxide nanopores requires an applied electric potential for anodization, which is typically set to match the pitch of nanoindentations on Al. This study reports a new voltage regime for Al anodization conditions where the process yields satellite pores of various shapes, periodicities, and sizes around the main pores. These new nanopatterned platforms provide an easy route to fabricate hierarchical metal nanostructures whose energy dispersions are shaped by the mode superposition of the surface plasmon polaritons originating from multiple periodic lattices.

In this study, we examined the dependence of surface morphology and spin Seebeck effect (SSE) voltages on the poly[vinylpyrrolidone] (PVP) concentration in polycrystalline Y3Fe5O12 (YIG) ultrathin films on a silicon substrate synthesized by metal-organic decomposition followed by a crystallization process. During fabrication, PVP concentrations of 0.5–2 g were used while all other conditions remained fixed. Atomic force microscopy and grazing incidence X-ray diffraction (XRD) measurements revealed a strong dependence of crystallinity and sample morphology on PVP concentration. The 1-g PVP sample had the smoothest surface, with a root mean square roughness of 0.2 nm, as well as superior bulk uniformity with respect to the shape and intensity of XRD reflection peaks. This was confirmed by scanning electron microscopy measurements of a cross-section of the sample that revealed a uniform film without pores. SSE measurements were performed to obtain the output SSE voltages (VSSE) of all samples, to which a platinum layer was added as a spin-detection layer. Repeatedly, the 1-g PVP sample had the best performance, demonstrating the importance of film crystallinity and morphology in the spin-to-charge conversion efficiency of YIG films.

Recently, the inherent piezoelectric properties of the 2D transition-metal dichalcogenides (TMDs) tin monosulfide (SnS) and tin disulfide (SnS2) have attracted much attention. Thus the piezoelectricity of these materials has been theoretically and experimentally investigated for energy-harvesting devices. However, the piezoelectric output performance of the SnS2- or SnS-based 2D thin film piezoelectric nanogenerator (PENG) is still relatively low, and the fabrication process is not suitable for practical applications. Here we report the formation of the SnS2/SnS heterostructure thin film for the enhanced output performance of a PENG using atomic layer deposition (ALD). The piezoelectric response of the heterostructure thin film was increased by ∼40% compared with that of the SnS2 thin film, attributed to large band offset induced by the heterojunction formation. Consequently, the output voltage and current density of the heterostructure PENG were 60 mV and 11.4 nA/cm2 at 0.6% tensile strain, respectively. In addition, thickness-controllable large-area uniform thin-film deposition via ALD ensures that the reproducible output performance is achieved and that the output density can be lithographically adjusted depending on the applications. Therefore, the SnS2/SnS heterostructure PENG fabricated in this work can be employed to develop a flexible energy-harvesting device or an attachable self-powered sensor for monitoring pulse and human body movement.

Rotor eccentricity occurs during manufacturing, causing the device to vibrate and make noise, thereby shortening its life. Its characteristics can be analyzed via the existing finite element method (FEM); however, analyzing characteristics according to design variables is time-consuming. Therefore, we implemented an analytical method that can rapidly identify the characteristics according to the design variables. We derived the magnetic flux density, the back-electromotive force, and the torque through the analytical method according to rotor eccentricity. The rotor eccentricity was considered to be based on the perturbation and the electromagnetic theories; accordingly, the governing equations and boundary conditions were derived. The analytical method was validated through FEM and experimental result.

Recently, the inherent piezoelectric properties of the 2D transition-metal dichalcogenides (TMDs) tin monosulfide (SnS) and tin disulfide (SnS

The evolution of "smart life," which connects all internet-of-things (IoT) microdevices and microsensors under wireless communication grids, requires microscale energy storage devices with high power and energy density and long-term cyclability to integrate them with sustainable power generators. Instead of Li-ion batteries with a short lifetime, pseudocapacitors with longer or infinite cyclability and high-power density have been considered as efficient energy storage devices for IoT. However, the design and fabrication of microscale pseudocapacitors have difficulties in patterning microscale electrodes when loading active materials at specific points of the electrodes using conventional microfabrication methods. Here, we developed a facile, one-step fabrication method of micro-supercapacitors (MSCs) through the in situ formation of Co metals and the reduced graphene oxides (rGOs) in a one-pot laser scribing process. The prepared Co/rGO MSC thus exhibited four times higher capacitance than the rGO MSC, due to the Faradaic charge capacitance behavior of the Co/rGO composites.

The current design trends in the field of electronic devices involve efforts to make these devices smaller, thinner, lighter, and more flexible. The development of such systems is expected to further accelerate, resulting in the production of wearable and Internet-of-Things devices. In this respect, microenergy storage systems with high capacity and fast charge/discharge rates have become important power sources for such devices. In particular, interdigitated microsupercapacitors (MSCs) have exhibited remarkable potential as micropower sources owing to their fast charge/discharge processes, long cycle life, and high power density compared with microbatteries. Nevertheless, facile fabrication of MSCs using interdigitated electrodes remains challenging, as it requires selective decoration of electrodes with pseudocapacitive materials, such as transition metal oxides, to increase their capacitance. In the present study, we developed a simple method for fabricating MSCs involving in situ formation of interdigitated graphene electrodes and ZnO nanorods by photothermal conversion of graphene oxide (GO) and Zn precursors using infrared (IR) laser scribing. The fabricated MSCs exhibit a high stack capacitance of 3.90 F cm−3 and an energy density of 0.43 mWh cm−3. Notably, the capacity of the developed material is three times higher than those of previously reported MSCs made from the same type of graphene. In addition, the capacitance retention rate of the fabricated MSC is approximately 70% when measured over 10,000 charging–discharging cycles at a constant current, which evidently indicates a stable device performance. Researchers in South Korea have developed a method for making tiny high-capacity energy storage devices. Portable electronic devices rely on light-weight sources of energy. Lithium ion batteries are the prevailing technology, but alternatives are being developed. Supercapacitors, for example, offer faster charging time and a longer life. Supercapacitors can be miniaturized by interlocking the electrodes, but such devices are difficult to fabricate. Junghyo Nah from the Chungnam National University, Daejeon, Min Hyung Lee from Kyung Hee University, Yongin, and colleagues have developed a simple method for making microsupercapacitors from graphene electrodes and zinc oxide nanorods. The capacity of their device was three times higher than that of previous microsupercapacitors built from the same type of graphene. The results could contribute to development of smaller, thinner and lighter power sources. Selective growth of ZnO nanorods/reduced graphene oxide composites via IR laser-induced reaction is developed for electrochemical devices. Optimized design of interdigitated supercapacitor electrodes can be achieved by programming of laser scanning lines. The integration of ZnO NRs on rGO improves supercapacitor performances due to synergistic effects of pseudo capacitance (ZnO) and electric double layer capacitance (graphene).

Performance enhancement of triboelectric nanogenerators (TENGs) has been largely limited by the relatively low output current density. Thus, extensive research efforts have been made to increase the output current density. In this respect, this work presents a method to effectively increase output current density of TENGs by adopting polarized ferroelectric polymers and MoS2 composite. Specifically, by compositing bulk MoS2 flakes with both Nylon-11 and PVDF-TrFE, respectively, charge density of each triboelectric charging surface was significantly increased. In addition, proper polarization of both ferroelectric composite layers has also led to an additional increase in the charge density. A combination of them synergistically increases the surface charge density, generating huge output current and the power output density. By optimizing the fabrication process, the output voltage and current density up to ∼145 V and ∼350 μA/cm2 are achieved, respectively. Consequently, the TENG exhibits a recordable output power density of ∼50 mW/cm2, which is one of the highest output power densities reported to date. The method introduced in this work can greatly increase the output current density of TENGs, facilitating the development of high-performance triboelectric energy harvesting devices.

There is a growing interest in window air filters to protect indoor air quality from ultrafine particulate matter (PM) in outdoor air. The filters for this purpose must achieve high filtering efficiency without compromising the original functions of the window, such as high air permeability and visibility. Several filters meeting these requirements have been developed and demonstrate a high PM

Ultrafine particulate matters (PMs) are an imminent threat to the human respiratory system, as their sizes are comparable to and even smaller than human tissues. To cope with this situation, researchers have developed and commercialized various personal dust proof masks. However, because of the relatively thick filter membrane to guarantee filtering efficiency, a huge pressure drop across the active filter layer is inevitable and breathing through it becomes uncomfortable. In this work, we investigated the performance of electrospun polybenzimidazole (PBI) nanofiber membrane filters that can potentially be used for dust proof masks or other high-performance filters. Thanks to its high dipole moment (6.12) as confirmed by density functional theory (DFT) calculation, the surface potential of the PBI nanofiber air filter, measured by KPFM, was higher than that of other commercially available mask filters. The filter developed in this work provides high PM filtering efficiency of ∼98.5% at much reduced pressure drop (130 Pa) in comparison to those used in commercially available masks (386 Pa) with similar filtering efficiencies. Consequently, an approximately 3-fold higher quality factor (∼0.032), evaluated for PM2.5, in comparison to that of commercial ones (∼0.011) was achieved by using PBI nanofiber. Furthermore, we developed a cleaning method effective for the filter contaminated by both inorganic and organic PMs. Even after several cycles of cleaning, the PBI filter membrane demonstrated negligible damage and retained its original performance because of its mechanical, thermal, and chemical durability.

Generally, triboelectric generators (TENGs) demonsrate a considerably lower output current than output voltage; this has largely limited their performance enhancement. Thus, enormous research efforts have been made to address this problem. In this work, we present a simple method to enhance the triboelectric output current by burying an indium zinc oxide (IZO) layer under the triboelectric polymer friction layer. The IZO layer provides large interface density of states, which function as a charge reservoir. During frictional contact-separation motion of the TENG, electrons can be stored in or pumped out of these states. By optimizing the properties of the IZO layer, the output performance of the TENG is greatly improved, generating an output power density of ~ 25 mW/cm2. Specifically, an output voltage and current density of ~ 140 V and ~ 180 μA/cm2 were obtained, which are 4-fold and 9-fold higher, respectively, than a TENG without an IZO layer. The method introduced here suffers less from friction layer wear-out and can effectively enhance the performance of TENGs.

We report the zinc/aluminum layered double hydroxides (Zn-Al:LDHs) nanosheets that were most facilely synthesized at room temperature via an environmentally friendly process and demonstrate their ability to convert mechanical deformation into an electrical stimulus by flexoelectricity. The 1 μm-thick Zn-Al:LDH nanosheets were most facilely synthesized for 2 h at room temperature after dipping the Al (10 at%)-doped ZnO (10AZO) (60 nm)/Au (10 nm)/10AZO (30 nm)-coated PET samples into the carbonated water that the CO2 in air was naturally captured in the water at room temperature. Based on the nanogenerators fabricated via facilely synthesized nanosheets, we observe a linear relationship between the output voltage and current generated by the centrosymmetric LDHs nanosheets and the curvature from bending, which is a direct evidence for flexoelectricity. We demonstrated the flexoelectric coefficient of our LDH nanosheet-based flexoelectric generators of 1.8 ± 0.35 μCm−1. The output power generated from the LDH nanosheet-based generators via a pushing shows higher performance than that from state-of-the-art flexoelectric PZT-MWCNT-based and piezoelectric BaTiO3 nanotubes-based generators. These findings could pave the way to the practical exploitation for environmentally friendly synthesis of LDH nanosheets using the CO2 in air and for harvesting the energy via LDH nanosheets-based generators.

Generation of electric potential by the flow of an electrolyte droplet on a graphene surface is investigated to develop a liquid motion energy harvester. Most of the research efforts to date have been focused on unveiling the interaction between graphene and an electrolyte droplet. However, other factors that significantly affect the output potential have not been paid much attention. Here, we report the electrostatic charging of graphene during a layer-transfer process and its influence on the enhancement of the performance of graphene-based liquid motion energy harvesting devices. In particular, we investigated the dependence of the output voltage on the triboelectric properties of the substrate. Our finding indicates that the triboelectric surface charging of graphene is significantly influenced by physisorption between graphene and the underlying substrate. Therefore, it directly affects the output power generation and the concentration of electrolyte solution at which the maximum power generation can be achieved. The method presented here is a simple route to further improve the output performance of graphene-based liquid motion energy harvesting devices and this study extends the physical understanding of charge interaction between graphene and an electrolyte solution.

The threshold voltages at the onset of conduction for electron and hole branches can provide information on band gap values or interface states in a gap. We measured conductivity of bilayer graphene encapsulated by hexagonal boron nitride as a function of back and top gates, where another bilayer graphene is used as a top gate. From the measured conductivity the transport gap values were extracted assuming zero interface trap states, and they are close to the theoretically expected gap values. From a little discrepancy an average density of interface states per energy within a band gap ( Dit) is also estimated. The data clearly show that Dit decreases as a bilayer graphene band gap increases rather than being constant. Despite the decreasing trend of Dit, interestingly the total interface states within a gap increases linearly as a band gap increases. This is because of ∼2 × 1010 cm-2 interface states localized at band edges even without a band gap, and other gap states are equally spread over the gap.

The dark current of long wavelength infrared (LWIR) detector should be reduced to improve performance and decrease the system size, weight and power consumption (SWaP). In this work, we present the process to reduce the dark current of T2SL LWIR detector with nBn structure. The nBn structure consists of InAs/GaSb 14/7 monolayers (MLs) contact layer and absorber separated by Al0.2Ga0.8Sb barrier. For T2SL LWIR detector, the barrier structure is often used to reduce the dark current and passivate absorber. However, the barrier itself is very fragile and easily damaged during the device process. The proposed process was developed so that Al0.2Ga0.8Sb barrier is not damaged by any solution from the isolation etch process to the passivation process. In this process, CHF3 plasma treatment after the isolation etch with ICP reduced significantly the dark current. We attribute this to damage reduction of Al0.2Ga0.8Sb barrier by CHF3 plasma treatment. The 15 μ m pitch devices fabricated with optimal process conditions showed the dark current density of less than 2.0 × 10−5 A/cm2 at −0.3 V and 80 K.

A novel design of electrically small, extremely thin, and horizontally polarized magnetic dipole antenna is proposed. It is composed of multiple folded arms packed in an extremely thin height of 0.0016λ, with the electrical size ka of 0.276. The radiation efficiency is 87% from the simulation. The radiation properties are investigated, and its operation as a small magnetic dipole antenna is confirmed. A three-dimensional printing technology is used for building the prototype due to the complexity of the proposed structure. The experimental results show good agreement with the computed expectation values.

For the development of high performance triboelectric generators (TENGs), it is required to have facile methods to adjust the triboelectric properties of the friction surfaces. In this work, we present the surface charge density modulation of the photopolymer–ferroelectric nanoparticle composite surface by applying ultraviolet (UV) and electric field. By using the photopolymer, the triboelectric surface property was modulated by exposure to UV. In addition, lithographic surface patterning can be easily adopted to enlarge the frictional surface area as well. Furthermore, the use of the PP allows a facile integration of ferroelectric nanoparticles (NPs) in the form of a nanocomposite structure, which can effectively increase the surface charge density by spontaneous dipole coupling of NPs embedded in the PP layer. As a result, approximately 4-fold higher output power has been achieved by applying this approach. The developed TENGs have also demonstrated superior mechanical durability, generating consistent outputs during 104 cyclic frictional contacts. The approach proposed here is a simple and reliable way to enhance the output performance of TENGs.

In this study, a combined system of microneedles and a triboelectric nanogenerator (TENG) has been developed for drug delivery. A triboelectric device, which converts mechanical energy into alternating current (AC), was chosen to replace the electrophoresis (EP) effect. To directly generate triboelectricity from salmon deoxyribonucleic acid (SDNA)-based microneedles, a triboelectric series of SDNA film and chargeable polymers (polyimide and Teflon) was studied. The electrical output of the two charged polymers was compared to find a material that could be highly charged with SDNA. The electrical output was also compared as a function of the concentration of a drug embedded in the SDNA film, and the results confirmed that drug intercalation affected the carrier diffusion. The mechanical strength of the microneedles was assessed by histological analysis of their penetration into porcine cadaver skin. Furthermore, the output voltage of a system incorporating microneedles and TENG in cadaver skin, and in vitro drug release into gelatin were evaluated to examine potential application as an electrically active drug delivery system. The electrical output voltage of this system was ∼95 V. The mechanism of triboelectric perturbation to the skin has also been discussed. The system developed in this work is a new, facile approach toward effective drug delivery that replaces the existing EP method and expands the application of TENGs.

We report high-performance piezoelectric nanogenerators (PENGs) with nanoimprinted sol–gel BaTiO3 (BTO) nanopillar array polarized under high electric field and ultraviolet. The PENGs fabricated using this method demonstrate greatly enhanced output voltage of ∼10 V and current density of ∼1.2 μA cm–2, respectively, in comparison to that of flat PENG. Further, the PENG demonstrates uniform output characteristics over the entire device area thanks to uniform nanoimprint pillar array. The approach introduced here is simple, effective, reliable, and reproducible way to fabricate high-performance sol–gel-based PENGs and electronic devices.

The barrier layer in InAs/GaSb LWIR nBn detector is usually composed of AlGaSb alloy, which has a non-negligible valence band offset and is sensitive to chemical solutions. In this work, we investigated a type-II superlattice (T2SL) barrier that is homogeneous with the T2SL absorber layer in order to resolve these drawbacks of the AlGaSb barrier. The lattice mismatch of the T2SL barrier was smaller than that of the AlGaSb barrier. At − 70 m V and 80 K, the dark current density and the noise equivalent temperature difference of the nBn devices with the T2SL barrier were 4.4 × 1 0 − 6 A / c m 2 and 33 mK, respectively.

As a new family member of two-dimensional layered materials, black phosphorus (BP) has attracted significant attention for chemical sensing applications due to its exceptional electrical, mechanical, and surface properties. However, producing air-stable BP sensors is extremely challenging because BP atomic layers degrade rapidly in ambient conditions. In this study, we explored the humidity sensing properties of BP field-effect transistors fully encapsulated by a 6 nm-thick Al2O3 encapsulation layer deposited by atomic layer deposition. The encapsulated BP sensors exhibited superior ambient stability with no noticeable degradation in sensing response after being stored in air for more than a week. Compared with the bare BP devices, the encapsulated ones offered long-term stability with a trade-off in slightly reduced sensitivity. Capacitance–voltage measurement results further reveal that instead of direct charge transfer, the electrostatic gating effect on BP flakes arising from the dipole moment of adso...

We report a simple method to realize multifunctional flexible motion sensor using ferroelectric lithium-doped ZnO-PDMS. The ferroelectric layer enables piezoelectric dynamic sensing and provides additional motion information to more precisely discriminate different motions. The PEDOT:PSS-functionalized AgNWs, working as electrode layers for the piezoelectric sensing layer, resistively detect a change of both movement or temperature. Thus, through the optimal integration of both elements, the sensing limit, accuracy, and functionality can be further expanded. The method introduced here is a simple and effective route to realize a high-performance flexible motion sensor with integrated multifunctionalities.

We measured the thermal conductivity of Araneus ventricosus' spider dragline silk using a suspended microdevice. The thermal conductivity of the silk fiber was approximately 0.4Wm-1K-1 at room temperature and gradually increased with an increasing temperature in a manner similar to that of other disordered crystals or proteins. In order to elucidate the effect of β-sheet crystals in the silk, thermal denaturation was used to reduce the quantity of the β-sheet crystals. A calculation with an effective medium approximation supported this measurement result showing that the thermal conductivity of β-sheet crystals had an insignificant effect on the thermal conductivity of SDS. Additionally, the enhancement of bonding strength in a glycine-rich matrix by atomic layer deposition did not increase the thermal conductivity. Thus, this study suggests that the disordered part of the glycine-rich matrix prevented the peptide chains from being coaxially extended via the cross-linking covalent bonds.